Phase locked loop clock source provided with a plurality of frequency adjustments

ABSTRACT

An oscillator circuit having a first programmable divider for obtaining a reference signal by dividing the frequency of an oscillation signal of a piezoelectric resonator by a frequency dividing number M. A PLL circuit using the reference signal as input thereto to obtain a multiplied signal, the multiplied signal being formed by multiplying the input signal by a second frequency dividing number N for a second programmable divider provided in a feedback circuit. A third programmable divider capable of dividing the frequency of the multiplied signal by a third frequency dividing number X and outputting the frequency-divided signal. The frequency dividing numbers M, N, and X can be set to values independent of each other. Therefore, innumerable combinations of the frequency dividing numbers M, N, and X can be used and the number of frequencies producible by one oscillator can be largely increased by enabling selection of any suitable one of such combinations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oscillator used as a clock sourceoscillation circuit for an information processor or a communicationprocessor and capable of supplying a signal used as a reference fordesired frequencies.

2. Description of Related Art

For use in information processors such as computers or in communicationapparatuses, an oscillator in which a piezoelectric resonator such as aquartz resonator is used as an oscillation source has been used as aclock source or the like. Each of processing sections forming aninformation processor is supplied with a clock signal or the like havinga suitable frequency on the basis of a signal supplied from such anoscillator. FIG. 18 shows an example of a conventional oscillator usinga PLL circuit. This oscillator 90 is arranged so as to be able to selectone of a plurality of frequencies predetermined to be output, and tooutput a signal having the selected frequency. The oscillator 90 has aquartz resonator 1, an oscillation signal output section 10 whichoscillates the quartz resonator 1 to output an oscillation signal φ1having a resonant frequency fc of the quartz resonator 1, a programmabledivider (reference divider: RD) 15 which divides (by M) the oscillationsignal φ1 to generate a reference signal φ2 having a frequency fr, a PLLcircuit 20 which operates by being supplied with this reference signalφ2, a programmable divider (output divider: OD) 30 which divides (by X)a multiplied signal φ3 output from the PLL circuit 20 and having afrequency fp to generate an output signal φ4 having a frequency fo, anda buffer 35 which amplifies and outputs the output signal φ4. The PLLcircuit 20 has a phase comparator 21 which compares the phase ofreference signal φ2 supplied from the RD 15 and the phase of a signalfed back from a voltage controlled oscillator (VCO) 23, a low-passfilter (LPF) 22 which cuts off high frequency components of an output ofthe phase comparator 21 and supplies the cut output to the VCO 23, andthe VCO 23 that oscillates so that the phases of the two signals inputto the phase comparator 21 coincide with each other. Further, a feedbackdivider (FD) 24 is provided in a feedback circuit of the PLL circuit.The frequency of an output of the VCO 23 is divided (by N) by the FD 24to be fed back to the phase comparator 21. Consequently, in the PLLcircuit 20, multiplied signal φ3 formed by multiplying the signal inputto the phase comparator 21 by N is output from the VCO 23.

Each of the dividers (frequency dividers) 15, 24, and 30 used in thisoscillator 90 is a programmable divider capable of dividing thefrequency of the input signal by a set frequency dividing number.Accordingly, in the oscillator 90 shown in FIG. 18, combinations offrequency dividing numbers M, N, and X for the frequencies to be outputare previously set in a memory 95, and one of the combinations of thefrequency dividing numbers M, N, and X stored in the memory 95 can beselected by a decoder 96 connected to an external input 94. For example,if the oscillator 90 uses a quartz resonator 1 having a resonantfrequency fc of 20 MHz, it can select and output one of sixteendifferent frequencies according to a combination of four externalterminals S0, S1, S2, and S3.

Use of a PLL oscillator using such a programmable divider has enabledone oscillator to cover a plurality of frequencies, thus making itpossible to provide an oscillator capable of operating as stably asconventional quartz oscillators in the period before a restrictedappointed limit of delivery. Recently, however, various requirementshave been posed for reference oscillation sources and there has been aneed to prepare various types of oscillators even if the above-describedPLL oscillator is used. Further, the speed of development of informationprocessors or communication apparatuses have been remarkably acceleratedand, therefore, a need for manufacturing oscillators of newspecifications or frequencies in a short period has arisen. On the otherhand, the operating accuracies of information processors andcommunication apparatuses have been improved, so that there is a need toalso improve the frequency accuracy of signals output from oscillators.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anoscillator which is capable of outputting an output signal that isstable and accurate in frequency in comparison with conventional PLLoscillators, which can be manufactured in a short period, and which canbe supplied at a low cost.

In the conventional PLL circuit, as described above, a quartz resonatorhaving a resonant frequency adjusted with a predetermined degree ofaccuracy is used and the resonant frequency is multiplied by apredetermined combination of frequency dividing numbers to obtain anoutput signal of an intended frequency. On the other hand, the inventorsof the present invention have found that output signals of variousfrequencies required by users can be obtained by setting the frequencydividing numbers for dividers to suitable values independent of eachother. That is, in an oscillator of the present invention, an outputsignal of a desired frequency can be obtained by enabling suitablesetting of frequency dividing numbers for dividers even if the resonantfrequency of a quartz resonator is not adjusted to an ideal value, andhigh-precision output signals adjusted to various frequencies requiredby users can be obtained regardless of whether or not they are to beoutput.

This will be described in more detail with reference to a model caseshown in FIG. 1. In FIG. 1, frequencies fp of an output signal(multiplied signal) from a PLL circuit are plotted, frequencies fp beingobtained by changing the value of frequency dividing number M for areference divider RD step by step from 5 to 10 and by changing the valueof frequency dividing number N for the FD of the PLL step by stepbetween 1 to 30 with respect to each value of frequency dividing numberM. It can be understood that, if the values of frequency dividingnumbers M and N can be variably set independent of each other in thismanner, various frequencies can be obtained from one resonant frequencyfc, as described below. For example, when the frequency dividing numberM is 10, frequencies fp of 0.1 fc and 0.2 fc can be obtained. Asfrequencies between these two frequencies, four frequencies of fc/9,fc/8, fc/7, and fc/6 can be obtained by suitably changing the frequencydividing numbers M and N. Thus, frequencies of the multiplied signaloutput from the PLL circuit can be set with very fine pitches by usingone quartz resonator. It is apparent that the pitches with whichfrequencies can be set can be made finer by increasing the frequencydividing number M for the reference divider RD. Conversely, even if aquartz resonator whose resonant frequency fc is different from the idealresonant frequency is employed, a multiplied signal of a desiredfrequency can also be obtained by suitably setting the frequencydividing numbers M and N.

Thus, the oscillator of the present invention is characterized bycomprising a piezoelectric resonator such as a quartz resonator, anoscillation signal output section for oscillating the piezoelectricresonator to output an oscillation signal of a first frequency, a firstprogrammable divider (reference divider: RD) for dividing the frequencyof the oscillation signal by a first frequency dividing number(frequency dividing number M) to obtain a reference signal of a secondfrequency, a PLL circuit section capable of operating by using thereference signal input thereto to obtain a multiplied signal of a thirdfrequency, the multiplied signal being formed by multiplying the inputsignal by a second frequency dividing number (frequency dividing numberN) for a second programmable divider (feedback divider: FD) provided ina feedback circuit, and a setting section capable of variably settingthe first and second frequency dividing numbers (frequency dividingnumbers M and N) to values independent of each other.

Further, a third programmable divider (output divider: OD) capable ofdividing the frequency of the multiplied signal by a third frequencydividing number (frequency dividing number X) may be provided and thesetting section may be arranged to variably set the third frequencydividing number (frequency dividing number X) to a value independent ofthe first and second frequency dividing numbers. In some case, this ODenables the frequency dividing number M for the RD to be set to asmaller number to set the frequency of the reference signal to a higherfrequency, thereby preventing deterioration of jitter as described belowas well as obtaining an output signal more stable in frequency.

As shown in FIG. 1, since integers are set as frequency dividing numbersM and N for frequency dividing with the programmable dividers,frequencies fp obtained by the PLL circuit are determined digitally(discretely) while the frequency dividing numbers M and N are suitablyset. Therefore, it is possible that there is no combination of frequencydividing numbers M and N for setting the obtained frequency withintolerance limits about the desired frequency. Also, there is a frequencyband G about a frequency corresponding to an integer multiple of theresonant frequency fc in which no frequency can be set with any settingof frequency dividing number M, N, or X changed variously as possible.If the maximum value of the frequency dividing number M is Mmax, thefrequency band G is as defined by ±fc/Mmax. The ranges of frequencybands G corresponding to ranges in which the frequency fp of themultiplied signal cannot be variably set for these reasons can belimitlessly restricted by increasing frequency dividing number M.However, if the frequency dividing number M is increased, the secondfrequency of the reference signal, i.e., the input signal to the PLLcircuit section, becomes so low that the signal obtained by multiplyingthis input signal while performing phase comparison is liable todeteriorate in accuracy and stability. That is, deterioration of jitteroccurs. Therefore, it is desirable to set the frequency dividing numberM below such a value that considerable deterioration of jitter isavoided.

In the oscillator of the present invention, therefore, an adjustmentcircuit capable of finely adjusting the first frequency with respect tothe resonant frequency of the piezoelectric resonator is provided in theoscillation signal output section to finely adjust the frequency of theoscillation signal, thereby ensuring that even a signal having afrequency which cannot be covered by only discrete setting of thecombination of frequency dividing numbers M and N, or which falls intothe frequency band in which no frequency can be set can be output fromthe oscillator. Moreover, since the frequency dividing number M islimited to a suitable value such that considerable deterioration ofjitter cannot occur, an output signal having high frequency accuracy andhigh stability can be obtained from the oscillator of this embodiment.The amount of adjustment by the adjustment circuit can be set in thesetting section together with the frequency dividing numbers M and N. Byvariably setting these values, any frequency required by a user can beoutput. Conversely, even if a quartz resonator not adjusted to an idealresonant frequency is used, a signal of the desired frequency can beoutput. Thus, there is no need for frequency adjustment of the quartzresonator itself and the oscillator can be set to any frequency requiredby a user after it has been manufactured, thus facilitatingmass-production of the oscillator. As a result, an oscillator capable ofobtaining an output signal having a desired frequency with improvedstability can be supplied in a very short period at a low cost.

As the adjustment circuit for finely adjusting the resonant frequency ofthe piezoelectric resonator in the oscillation signal output section, acircuit having a plurality of weighted capacitance arrays may be used. Acircuit having a variable-capacitance diode is also available. Each ofthese circuits enables the adjustment amount to be set as a digitalvalue and therefore enables the adjustment amount to be stored and setin the setting section together with the frequency dividing numbers Mand N. To store these frequency dividing numbers M and N, frequencydividing number X, or the adjustment amount in the setting section, aROM (read only memory) may be used. If a change with time, resettingafter setting these values, and enabling the memory to be used withsuitable set values for inspection are taken into consideration, it isdesirable to use an EPROM, i.e., rewritable ROM, as the above-mentionedROM. However, the oscillator may have the piezoelectric resonator, theoscillation signal output section, the first programmable divider, thePLL circuit section and the setting section packaged integrally witheach other and covered with a mold resin. If the oscillator uses suchpackaging, the EPROM cannot be irradiated with ultraviolet rays. On theother hand, an EEPROM or the like may be used. In such a case, however,the control system becomes complicated and high-priced. In theoscillator of the present invention, therefore, the arrangement may besuch that a plurality of ROMs are provided in the setting section toenable at least the first and second frequency dividing numbers (M andN) or the amount of adjustment to be set in each of the ROMs. Thus, anoscillator can be provided which is simple in structure and low-pricedbut capable of resetting frequency dividing number M or N, theadjustment amount or the like.

An input section for controlling the operating state of the oscillatormay be provided and information designating a function controllable bythe input section may be stored in this ROM.

Further, to enable the oscillator to be set so that an output signal ofthe desired frequency can be obtained after the piezoelectric resonator,the oscillation signal output section, the first programmable divider,the PLL circuit section and the setting section have been packagedintegrally with each other, it is desirable that the resonant frequency,i.e., the first frequency of the oscillation signal not yet adjusted bythe adjustment circuit, should be measurable. For such an effect, thefrequency obtained by setting each of frequency dividing numbers M, N,and X to 1 may be measured. However, it is desirable to provide a bypasscircuit for enabling direct measurement of the oscillation signalbypassing the first programmable divider and the PLL circuit section.

Most of frequencies required to be supplied by the oscillator are thosebased on 32.768 kHz for communication or 33.333 kHz for systematic uses.A rectangular AT cut quartz resonator manufactured to oscillate afundamental wave at 25.1 MHz produces the base of frequencies forsystematic uses when the frequency dividing number M is 753, and thebase of communication frequencies within a range in which adjustment canbe easily performed by an adjustment circuit of about 10 ppm whenfrequency dividing number M is 766. Further, this quartz resonator is aresonator which can be manufactured at a low cost, which is free fromcoupling with spurious vibration, and which has a high yield.Consequently, it can be understood that almost all of the frequenciescan be covered by using a quartz resonator of 25.1 MHz.

To set a frequency in the oscillator of the present invention, a methodmay be used in which, on the basis of the unadjusted resonant frequencymeasured by using the above-mentioned bypass circuit or the like, thefirst and second frequency dividing numbers are set to such numbers thatthe third frequency of the multiplied signal is obtained as a frequencyclosest to the desired frequency. Then, fine adjustment is performed sothat the third frequency becomes equal to the desired frequency. In thismanner, the oscillator can be set so as to output a signal having thedesired frequency without performing frequency adjustment of thepiezoelectric resonator itself. Needless to say, if it is desirable toperform frequency dividing in the third programmable divider (OD), thethird frequency may be set to a frequency by considering a frequencydividing number X.

Another method may also be used in which, with respect to the desiredfrequency, the first and second frequency dividing numbers with which anoutput signal having the closest third frequency can be obtained arepreviously calculated on the basis of the ideal resonant frequency ofthe piezoelectric resonator, and the first frequency is finely adjustedon the basis of the first and second frequency dividing numbers to sucha value that the desired frequency is obtained.

Such oscillation frequency setting operation s may be performed solelybefore the oscillator is mounted on a circuit board. Alternatively,setting operations may be performed after the oscillator has beenmounted on a circuit board. Further, frequency setting operations can beperformed before, after or simultaneously with the process forinspection using probes connected to the circuit board. If frequencysetting operations are performed after mounting the oscillator on acircuit board, the oscillation frequency can be set by reflecting asubtle change in the state of the resonator or the like caused bymounting on the circuit board. If such setting operations are performedbefore, after or simultaneously with the inspection process, theoperation process can also be shortened. In a case of a conventionaloscillator in which an oscillation frequency is uniquely determined onthe maker side is used, no frequency setting operations are performed onthe user side. Similarly, with respect to the oscillator of the presentinvention, oscillation frequency setting may be performed as stepsintegral with the sequence of inspection operations. In this manner, theoscillator of the present invention cap able of variably changing theoscillation frequency is assembled and frequency-adjusted by the samenumber of steps or the same procedure as that for conventionaloscillators in which the oscillation frequency cannot be changed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing is a model of a frequency distribution of asignal producible by an oscillator of the present invention.

FIG. 2 is a block diagram schematically showing the configuration of anoscillator which represents an embodiment of the present invention.

FIG. 3 is a perspective view of an external appearance of the oscillatorshown in FIG. 2.

FIG. 4 is a diagram showing the internal structure of the oscillatorshown in FIG. 3 with a mold partially removed.

FIG. 5 is a table showing a part of the examples of frequency dividingmembers M, N, and X which can be set in the oscillator shown in FIG. 2.

FIG. 6 is a diagram showing an adjustment circuit using capacitancearrays.

FIG. 7 is a diagram showing an adjustment circuit using avariable-capacitance diode.

FIG. 8 is a flowchart showing an example of the process of setting afrequency of the oscillator shown in FIG. 2.

FIG. 9 is a flowchart showing another example of the process of settinga frequency of the oscillator shown in FIG. 2.

FIG. 10 is a diagram showing an example of frequency setting accordingto the method shown in FIG. 9.

FIGS. 11(a)-(c) are diagrams showing another example of the oscillatorof the present invention, FIG. 11(a) being a cross-sectional view in adirection along a plane, FIG. 11(b) being a longitudinal cross-sectionalview, FIG. 11(c) being a cross-sectional view in a lateral direction.

FIG. 12 is a diagram showing an oscillator using a ceramic case, whichis still another example of the oscillator of the present invention.

FIG. 13 is a diagram showing an oscillator using a metallic case, whichis a further example of the oscillator of the present invention.

FIG. 14 is a diagram showing an ultraviolet erase type oscillator, whichis a further example of the oscillator of the present invention.

FIG. 15(a) is a diagram showing a state where t he oscillator shown inFIG. 14 is realized as SMD, and FIG. 15(b) is a diagram showing a statewhere it is realized as DIP.

FIG. 16 is a diagram showing a further example of the oscillator of thepresent invention, constructed on a circuit board.

FIG. 17 is a flowchart showing the process of performing frequencyadjustment of an oscillator mounted on a circuit board.

FIG. 18 is a block diagram showing an example of a conventionaloscillator.

FIG. 19 is a diagram showing frequencies each of which can be outputfrom the oscillator shown in FIG. 18.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings. FIG. 2 shows an embodiment of an oscillatorusing a PLL circuit of the present invention. The oscillator 5 of thisembodiment also outputs an output signal φ4 having a predeterminedfrequency to by oscillating a quartz resonator 1 and by performingmultiplication in the PLL circuit. Portions corresponding to those ofthe oscillator described with reference to FIG. 18 are indicated by thesame reference numerals and detailed description for them will not berepeated. In the oscillator 5 of this embodiment, an oscillation signaloutput section 10, which oscillates the quartz resonator 1, has, inaddition to an oscillation circuit 11, an adjustment circuit 12 capableof changing a frequency fg of an oscillation signal φ1 by finelyadjusting a resonant frequency fc of the quartz resonator 1. Thefrequency of the oscillation signal φ1 finely adjusted is divided by Mby a reference divider (RD) 15, which is a programmable divider, to forma reference signal φ2 having a frequency fr. Reference signal φ2 issupplied to a PLL circuit 20. The PLL circuit 20 operates by beingsupplied with the reference signal φ2 and outputs a multiplied signal φ3which is obtained by multiplying the reference signal φ2 by a frequencydividing number N by a feedback divider (FD) 24 provided as aprogrammable divider in a feedback circuit, and which has a frequencyfp. This multiplied signal φ3 is further divided by X by an outputdivider (OD) 30, which is a third programmable divider, to form anoutput signal φ4 having a frequency fo. Output signal φ4 passes aselector 32 and a buffer 35 to be output through an output terminal 61.The selector 32 is for changing the output signal φ4 and a bypasscircuit 36 for directly outputting through the output terminal 61 theoscillation signal φ1 output from the oscillation signal output section10. The selector 32 is controlled by a setting section 40 describedbelow. Further, the buffer 35 has a function of buffering andamplifying, and outputting the output signal φ4 and thereafteroutputting the amplified signal, and a function of setting the outputterminal in a high-impedance state according to an operation mode of theoscillator.

These dividers RD 15, FD 24, and OD 30, the adjustment circuit 12, andso on are supplied with frequency dividing numbers M, N, and X, anadjustment amount, and so on. The setting section 40 of this embodimenthas ROMs 41 and 42 forming two stages, and a shift register 43 capableof converting input serial data into parallel data to write the data ineach of the ROMs 41 and 42. This shift register 43 is also used totemporarily set an amount of adjustment performed by the adjustmentcircuit 12 or to temporarily set the frequency dividing numbers M, N,and X. The setting section 40 further has a control circuit 44 whichcontrols the buffer 35 and the selector 32 through the ROMs 41 and 42and controls writing of data to the ROMs 41 and 42. Selection of controlmodes of the control circuit 44 is performed through a control terminal62. For example, to write data to the ROM 41 or ROM 42 through the shiftregister 43, the output terminal 61 is used as a data input terminal.Accordingly, at the time of data writing, the buffer 35 is closed anddata input from the output terminal 61 is sent to the shift register 43via the control circuit 44 and is converted into parallel data to bewritten to the ROM 41 or 42. In the oscillator 5 of this embodiment,therefore, no decoder is provided and values freely set independent ofeach other can be stored in the ROM 41 or 42 as frequency dividingnumbers M, N, and X and an adjustment amount, and the values can bechanged freely. Needless to say, predetermined combinations of frequencydividing numbers M, N, and X and adjustment amounts can be externallyloaded as data in the ROM 41 or 42. In the oscillator 5 of thisembodiment, such combinations are not exclusively used, and frequencydividing numbers M, N, and X and the adjustment amount can be set tovarious values freely and independently according to one's need.

The ROMs 41 and 42 can be used by being changed by the control circuit44. The PLL circuit and the dividers operate with set values stored inthe ROM 41 or 42. Each of the ROMs 41 and 42 of this embodiment has sucha capacity as to be able to store all data necessary for controlling theoscillator 5 of this embodiment, e.g., frequency dividing numbers M, N,and X, and adjustment amounts. If a change in the resonant frequency fcof the quartz resonator results as a change with time or the like, or ina case where the oscillator 5 of this embodiment is used as anoscillation source for a signal of a frequency different from afrequency initially set, frequency dividing numbers M, N, and X, theadjustment amount, and so on can be reset.

Needless to say, use of the ROMs 41 and 42 is not limited to this. Forexample, they may also be used to enable a maker to collectively performinspections requiring special skills with respect to characteristics ofthe oscillator by writing inspection data to the ROM 41 on the makerside. Objects of such inspections are PLL lockup characteristic, therelationship between the power supply voltage and the rise time ofoscillation, and so on. It is difficult for a user to perform suchinspections for reasons relating to the equipment and techniques. It is,therefore, desirable that such inspections should be performed on themaker side by specialist engineers using inspection apparatuses havinghigh-performance measuring ability.

In the oscillator 5 of this embodiment, even if the ROM 41 is used toperform such inspections, the other ROM 42 can be freely used on theuser side. Accordingly, only good articles which have passed inspectionsare shipped from a maker, and data corresponding to certain requirementsis written to the ROM 42 at a business station or by a user. Since thereis no need to again inspect the items inspected on the maker side,simpler inspections will suffice on the business station or user side.

Further, in the oscillator 5 of this embodiment, since the ROMs 41 and42 are used as a set value storage medium, one of functions OE, ST andSTZ controllable through the control terminal 62 in functions capable ofcontrolling the operating state of the oscillator 5 can be set in theROMs. The OE (output enable) function is a function for setting theoutput signal φ4 in a high-impedance state while operating theoscillation circuit for quartz resonator 1 and the PLL circuit. Thisfunction is used at the time of an operation test of a computer or thelike. The ST (standby) function is a function for fixing the outputsignal φ4 at a high level or low level by setting the oscillationcircuit and the PLL circuit in a stopped state. This function iseffective in saving energy in a computer or the like. The STZ functionis a function based on a combination of the two functions, i.e., afunction for setting the output signal φ4 in a high-impedance statewhile stopping the oscillation circuit and the PLL circuit. Therefore,this function can be used at the time of an operation test when acomputer is manufactured and at the time of energy saving. Further, datafor setting the duty of a signal output from the output terminal 61 asdesired is stored in the ROMs 41 and 42.

In the oscillator 5 of this embodiment, the oscillation signal outputsection 10, the divider RD 15, the PLL circuit 20, the divider OD 30,the selector 32, the buffer 35 and the setting section 40 are combinedin one chip forming an IC 60. This IC 60 and quartz resonator 1 arepackaged by molding. FIG. 3 shows an external appearance of theoscillator 5 of this embodiment in a state of being packaged with a moldresin 68, and FIG. 4 shows the internal structure of the oscillator withmold resin 68 partially removed. In the oscillator 5 of this embodiment,IC 60 is mounted on one of two surfaces of a lead frame 67 while quartzresonator 1 enclosed in a cylinder is mounted on the other surface ofthe lead frame 67. These are packaged integrally with each other withmold resin 68, the output terminal 61, and the control terminal 62, thatis also used as an essential terminal for the oscillator appearingoutside the package. The terminal for writing data may be provided so asto be also used as an essential terminal for the oscillator or may beprovided for its special function only. Even if an EPROM is used as ROM41 or 42, it is covered with mold 68 and cannot be irradiated withultraviolet rays since the ROMs 41 and 42 are packaged. An EEPROM or thelike may be used. In such a case, however, the control circuit 44becomes further complicated and the ROM is high-priced. In contrast, ifROMs 41 and 42 in two arrays having a sufficiently large capacity areprepared like those in the oscillator 5 of this embodiment, ROMs 41 and42 can be used by being changed and it is possible to reliably rewriteor change set values including frequency dividing numbers at a low cost.

In the oscillator 5 of this embodiment, a rectangular AT cut quartzresonator manufactured so as to oscillate a fundamental wave at 25.1 MHzis used as quartz resonator 1. This quartz resonator is the most stableone of piezoelectric resonators considering physical and chemicalchanges, and even changes with time. It is possible to realize anoscillator having improved reliability by using a quartz resonator.Further, the vibrating piece may be formed into a rectangular shape tobe more compact than disk-like vibrating pieces, thereby enabling theoscillator to be reduced in size. Since a rectangular AT cut quartzresonator for oscillation of a fundamental wave at 25.1 MHz can berealized, oscillation can be achieved with improved stability incomparison with oscillation of resonators having resonant frequencieshigher than 30 MHz and oscillating in overtones.

Further, since the quartz resonator 1 of this embodiment is a quartzresonator oscillating a fundamental wave, its frequency variable rangeis very wide and the frequency of oscillation signal φ1 can be set in awide range by the adjustment circuit 12 of the oscillation signal outputsection 10. In the oscillator 5 of this embodiment, frequency dividingnumbers M and N are digital values, as described above with respect tothe model shown in FIG. 1. Therefore, the frequency fp obtained by thePLL circuit 20 is a discrete value even if the frequency dividingnumbers M and N are changed. Also, a frequency band G which has apredetermined width and in which no frequency can be set exists abouteach of frequencies corresponding to integer multiples of frequency fgof the oscillation signal φ1 or frequency fc even if the frequencydividing numbers M and N are changed. On the other hand, the quartzresonator 1 of this embodiment has a wide frequency variable range suchthat the amount of adjustment performed by the adjustment circuit 12 canbe increased. Therefore, even in a case where a predetermined frequencyfo cannot be obtained according to the combination of the frequencydividing numbers M and N, output signal φ4 having the predeterminedfrequency fo can be reliably generated by finely adjusting the frequencyof the oscillation signal φ1 on the adjustment circuit 12 side.

Further, while resonators of 20 MHz or lower require convex working forconfining energy, the 25.1 MHz resonator of this embodiment can berealized in a rectangular form. Thus, a high-quality resonator can beprovided at a low cost. Moreover, since there is no coupling withspurious vibrations in a wide range about 25.1 MHz, the yield is high.Also for this reason, a low-priced high-quality resonator can beprovided. The oscillator 5 of this embodiment can generate outputsignals having various frequencies by variably setting the frequencydividing numbers M, N, and X to suitable values and can therefore beadapted generally to all frequencies presently required by users if sucha high-quality, small, low-priced quartz resonator 1 is used as anoscillation source. Most of frequencies presently in demand are thosebased on 32.768 kHz for communication or 33.333 kHz for systematic uses.A rectangular AT cut quartz resonator manufactured to oscillate afundamental wave at 25.1 MHz produces the base of frequencies forsystematic uses when the frequency dividing number M is 753, and thebase of communication frequencies within a range in which adjustment canbe easily performed by an adjustment circuit of about 10 ppm when thefrequency dividing number M is 766. Consequently, it can be understoodthat almost all of the frequencies can be covered by using a quartzresonator of 25.1 MHz.

FIG. 5 shows cases of combinations of frequency dividing numbers M, N,and X usable in the oscillator 5 of this embodiment to obtain an outputsignal φ4 having frequency fo of 16 MHz by using a quartz resonator 1having resonant frequency fc of 25.1 MHz. As can be understood from thistable, a frequency having a deviation of about several 10's to several100's ppm from 16 MHz set as a target can be obtained with theoscillator 5 of this embodiment by setting suitable frequency dividingnumbers M, N, and X about the combination of frequency dividing numbersM, N, and X shown as cases 4, 5 or 6. Conversely, in a case where thequartz resonator 1 having a deviation of about several 10's to several100's ppm from the ideal resonant frequency of 25.1 MHz is used, thesefrequency dividing numbers M and N may be set in the ROM 41 or 42 toobtain the desired 16 MHz output signal φ4. Thus, in oscillators 5 ofthis embodiment, each of the resonators in the state of havingexcitation electrodes attached to a vibrating piece may be directly usedby setting the frequency diving numbers M and N suitable for theresonant frequency of the resonator to obtain an output signal φ4 havingthe desired frequency fo without specially adjusting the resonantfrequency of the quartz resonator 1 to the ideal target value, e.g.,25.1 MHz with accuracy. Therefore, the need for operations of weightremoval and weight addition for frequency adjustment can be eliminatedand troublesome steps using such operations can be removed.Simultaneously, the problem of a deterioration in characteristics or afrequency shift due to a position error or unbalance resulting fromweight removal or weight addition can be solved. Further, it is possibleto absorb an error in frequency due to a variation in circuit constantsof the oscillation circuit 11 or the like by selecting a suitablefrequency in each oscillator 5. As a result, the oscillator 5 of thisembodiment can obtain an output signal highly accurate and stable infrequency without requiring substantially troublesome operations inmanufacture, assembly and adjustment.

Since the values of frequency dividing numbers M, N, and X selectable inthe oscillator 5 of this embodiment are integers, the obtained frequencyfo has a discrete value. Conversely, with respect to a certain value ofthe resonant frequency of the quartz resonator 1, there is a possibilityof failure in finding suitable integer values as the frequency dividingnumbers M, N, and X. Also, in some case, with respect to a certain valueof the desired frequency fo, there is a possibility of an occurrence ofthe above-mentioned frequency band G about a frequency corresponding toan integer multiple of the resonant frequency fo in which adjustmentcannot be performed even if the frequency dividing number M, N, or X arechanged. On the other hand, if the frequency dividing number M for RD 15for forming reference signal φ2 is increased, cases in which adjustmentcannot be performed are effectively reduced, as described above withreference to FIG. 1. However, if the frequency dividing number M isincreased, a deterioration of jitter of the multiplied signal φ3obtained by the PLL circuit 20 is also increased, as described above.Therefore, it is desirable that, with respect to the resonant frequencyfc of the quartz resonator, a combination of frequency dividing numbersM, N, and X be selected such that frequency dividing number M isminimized. In this embodiment, to cope with such cases, the adjustmentcircuit 12 capable of finely adjusting the frequency fg of theoscillation signal with respect to the resonant frequency fc obtained bythe oscillation circuit 11 is provided in the oscillation signal outputsection 10. In a case where the maximum value Mmax of the frequencydividing number M is set to, for example, 800, it is desirable that, byconsidering occurrence of a frequency band G of 1250 ppm about theresonant frequency fc in which the desired frequency cannot be set bychanging the frequency dividing numbers M and N, the range in which thefrequency can be adjusted by the adjustment circuit 12 should beselected such that the adjustment circuit 12 can perform fine adjustmentto such a maximum extent as to cover the frequency band G at themaximum. Alternatively, a suitable integer, e.g., 2 or 3 may be set asthe frequency dividing number X for the OD 30 to reduce the width of thefrequency range in which the desired frequency setting cannot beperformed to 1/2 or 1/3, thereby restricting the range in whichadjustment should be performed by the adjustment circuit 12 inconnection with the oscillator circuit 11.

FIGS. 6 and 7 show examples of the adjustment circuit 12. Theoscillation circuit 11 has an inverter 11b, a feedback resistor ala, adrain resistor 11c, a drain capacitance lid, and a gate capacitance 11f,and is arranged so as to be able to adjust the frequency fg ofoscillation signal φ1 by changing the capacitance of the gatecapacitance 11f by means of the adjustment circuit 12. Accordingly, inthe adjustment circuit 12 shown in FIG. 6, n weighted capacitance arrays13.1 to 13.n are connected in parallel with the gate capacitance of, andtransistor switches 14.1 to 14.n respectively connected to thecapacitance arrays 13.1 to 13.n are turned on or off to variably set thecapacitance of the gate capacitance 11f. The amount of adjustment isstored in the ROM 41 or 42 of the setting section 40 as digital data forturning on or off the transistor switches 14.1 to 14.n. In the exampleof the adjustment circuit 12 shown in FIG. 7, a variable-capacitancediode 19 is used. The capacitance of the variable-capacitance diode 19connected to gate capacitor of via a capacitor 17 is controlled in adigital manner through a D/A converter 18. The amount of adjustment bythe variable-capacitance diode 19 is stored in the ROM 41 or 42 of thesetting section 40 as is that in the former example.

FIGS. 8 and 9 show methods of setting the frequency fo of the outputsignal φ4 of the oscillator 5 of this embodiment to a desired value. Inthe frequency setting method shown in FIG. 8, the resonant frequency fcof quartz resonator 1 in an unadjusted state is first measured in step71. In the oscillator 5 of this embodiment, the bypass circuit 36 isprovided for this measurement. The signal of resonant frequency fc canbe measured through the external terminal 61 by oscillating the quartzresonator 1 in a state where adjustment is not performed by theadjustment circuit 12. The resonant frequency fc can also be measured bysetting each of the frequency dividing numbers M, N, and X for thedividers RD 15, FD 24 and OD 30 to 1 by using the shift register 43 ofthe setting section 40. This measurement can be performed without usingthe bypass circuit 36. The arrangement using the bypass circuit 36 toenable the resonant frequency to be immediately measured is particularlyeffective in grasping the quality of the frequency source, analyzing adefect, and the like. Next, in step 72, suitable frequency dividingnumbers M and N are calculated from the value of resonant frequency fcand the desired output frequency fo. If necessary, the frequencydividing number X is also calculated simultaneously. At this time, toprevent deterioration of jitter, a method may be used, for example, amethod in which the smallest possible value of the frequency dividingnumber M is selected within a range such that the desired adjustment canbe performed by the adjustment circuit 12, or a method in which thefrequency dividing number M is selected by being brought close to alimit value to minimize the amount of adjustment. In the oscillator 5 ofthis embodiment, there is no need for determining a unique combinationof frequency dividing numbers M, N, and X with respect to the frequencyfo of the output signal, and the frequency dividing numbers M and N cantherefore be determined under conditions according to a user's purposeor the like.

After frequency dividing numbers M and N have been determined, thefrequency dividing numbers M and N and so on are set in the shiftregister 43 or the like in step 73. While the frequency fg ofoscillation signal φ1 is being finely adjusted by the adjustment circuit12 in step 74, a check is made in step 75 as to whether the desiredvalue of the frequency fo of output signal φ4 has been obtained. Steps74 and 75 are repeated until the desired frequency is obtained. If thisfrequency setting method is used, the frequency adjustment step forbringing the resonant frequency of quartz resonator 1 closer to acertain ideal value can be removed from the process of manufacturingquartz resonator 1. Thus, a quartz resonator supplied in a short periodat a low cost can be used in the oscillator 5 of this embodiment.Moreover, in the oscillator 5 of this embodiment, frequency dividingnumbers M, N, and X and an adjustment amount can be suitably determinedaccording to the resonant frequency fc of the quartz resonator 1 and thefrequency fo required by a user, and can be variably set to independentvalues. There is no need to select frequency dividing numbers M, N, andX and an amount of adjustment from combinations prepared in a memory,which operation has been necessary with respect to conventionaloscillators. Consequently, the oscillator of this embodiment can beshipped after being packaged with IC 60 and quartz resonator 1, molded,and after being set to a frequency required by a user. Therefore, it ispossible to produce oscillators to meet a prospective demand no matterwhat frequencies are required by users. Thus, the form of the oscillator5 of this embodiment is markedly suitable for mass production. Thus, theoscillator 5 of any frequency required by users can be supplied in ashort period at a low cost.

The frequency setting method shown in FIG. 9 is a method for adjustingoscillation of quartz resonator 1 at the resonant frequency fc by thecontrol adjustment circuit 12 to set the oscillation frequency fg at theoutput point of the oscillation circuit 11 to the ideal frequency of thequartz resonator 1, or to set it to a frequency necessary when frequencydividing numbers M, N, and X are set to a predetermined combination ofvalues with respect to the frequency fo required by a user.

First, in step 81, frequency dividing numbers M, N, and X most favorablein obtaining the desired output frequency fo on the basis of the idealquartz resonator frequency fci without a tolerance are determined. FIG.10 shows an example of the case of obtaining 106.25 MHz as the desiredoutput frequency fo when the resonant frequency fe of the quartzresonator has a variation of about 10000 ppm from 25.100000 to 25.351000MHz. The original resonant frequency fc can be obtained from theoscillation frequency (resonant frequency) fg in the unadjusted state bysetting the bypass circuit 36 or all the frequency dividing numbersto 1. In the case shown in FIG. 10, the range from 25.100000 to25.351000 MHz is divided into 56 intervals with a 180 ppm pitch suchthat the frequency is suitably adjustable with the capacitance arrays.From the obtained resonant frequency fc, the interval to which theresonator corresponds is determined. If the obtained resonant frequencyfc is 25.105 MHz, the quartz resonator corresponds to the interval 2.

Next, in step 82, the capacitance arrays are adjusted so that theoscillation frequency fg becomes equal to a frequency representing theinterval 2, i.e., a frequency of 25.104518 MHz at which M and N suitablefor obtaining the output frequency fo are determined. In step 83, thisfrequency fg is identified. Steps 82 and 83 are repeated until theoscillation frequency fg becomes equal to the above-mentioned frequencyof 25.104518 MHz representing the interval 2.

When the oscillation frequency representing the interval is obtained,the combination of frequency dividing numbers M, N, and X previouslycomputed, i.e., the combination of M=551, N=2332 and X=1, is set in theROM. As a result, output signal φ4 of the desired frequency fo (106.25MHz in this example) is obtained in accordance with the above-describedrelationship, i.e., the relationship shown by the following equation(1):

    fo=fg×(N/M)/X                                        (1)

The oscillator 5 in which quartz resonator 1 and IC 60 are packaged withmold resin 68 in the state of being superposed on each other in thedirection of thickness with lead frame 67 interposed therebetween hasbeen described by way of example. Needless to say, the package of theoscillator 5 is not limited to such a package. Quartz resonator 1 and IC60 may be packaged by using a mold resin while being placed adjacent toeach other along a plane, as shown in FIGS. 11(a)-(c), thereby providinga thinner oscillator 5.

Further, another oscillator 5 may be supplied which uses, as shown inFIG. 12, a ceramic case 63 in which IC 60 is accommodated in a ceramicbase 63a, and a vibrating piece la of a quartz resonator is accommodatedin a cantilevered state, and which is thereafter capped with a ceramicor metallic lid 63b. Since there is no need for a special case foraccommodating the vibrating piece la in this oscillator 5, an oscillator5 further reduced in size and thickness in comparison with thosedescribed above can be provided.

Needless to say, an oscillator 5 having a vibrating piece la and IC 60accommodated in a metallic case 64 as shown in FIG. 13 may also beprovided. The type of oscillator using such metallic case 64 is wellknown. The oscillator 5 of this embodiment of the present invention canalso be realized as such a conventional type.

Further, as shown in FIG. 14, a transmission window 65 formed of a glassor the like for transmission of ultraviolet rays may be provided at aposition corresponding to the IC 60 at the time of packaging, therebyenabling use of the IC 60 incorporating an EPROM capable of erasingrecorded data with ultraviolet rays. In this manner, an oscillator 5 canbe provided in which data in a ROM can be used by being rewritten if adesign change is made according to a user's need, and which can be usedmore flexibly. The method of erasing data by using ultraviolet rays doesnot require any special skill, is free from the risk of impairing otherfunctions of the oscillator in contrast with data erasing method usingelectrical means, and therefore enables reliable processing.

An oscillator 5 provided by such a packaging method can also be realizedas a surface mount type device (SMD) such as shown in FIG. 15(a) or adip type (DIP) such as shown in FIG. 15(b).

The oscillator of the present invention also comprises an oscillator 5having a structure, such as that shown in FIG. 16, in which the quartzresonator 1 and IC 60 are respectively mounted on a substrate (circuitboard) 66 without being packaged with a mold resin or the like. Anoscillator 5 having an IC 60 and resonator 1 separately mounted in sucha manner can be arranged by a user using a resonator having acharacteristic or shape according to use and so on. In this manner, amore flexible system can be formed.

In the oscillators 5 in which the quartz resonator 1 and IC 60 arepackaged integrally with each other, as well as in the oscillator 5shown in FIG. 16, in which the quartz resonator 1 and IC 60 are mountedon circuit board 66 separately from each other, frequency setting can beperformed after each oscillator 5 has been mounted on circuit board 66,and data of this setting may also be written in the ROM of the IC 60. Itis also possible to perform frequency setting operations simultaneouslywith or before or after inspection of the circuit board 66.

It is possible that the output frequency of each oscillator 5 adjustedin a single state and the output frequency of the oscillator 5 in thestate of being mounted on circuit board 66 differ slightly from eachother. If frequency setting is performed after mounting of theoscillator 5 on the circuit board 66, there is no possibility of anoccurrence of such a variation in output frequency, and a signal can beobtained with improved accuracy.

The oscillator 5 in accordance with the present invention can be set toa suitable frequency required by a user. Needless to say, operations forthis setting may be performed on the maker side and may also beperformed on the user side. The setting can be immediately adapted tothe design of a system or a change in the system. In such a case,however, a new operation for setting a frequency on the user side mustbe performed, resulting in an increase in the number of process steps.On the other hand, it is possible to perform a sequence of steps, suchas shown in FIG. 17, i.e., the step of mounting oscillator 5 on thecircuit board (step 111), the step of connecting probes 101 to a circuitor to special pads 105 on circuit board 66 for the purpose of circuitboard inspection (step 112), the step of performing circuit boardinspection (step 113), and the step of performing frequency setting bythe process shown in FIG. 8 or 9 (step 114). If such a frequency settingmethod is used, the oscillator of the present invention can be assembledand shipped by the same process as that for the conventional oscillatorsin which frequencies are uniquely determined.

If such a frequency setting method is used, it is desirable to use afrequency setting apparatus 100 having probes 101 connectable to thepads or the circuit connected to the oscillator 5 on the circuit board,and having the functions of determining an amount of adjustment ofcapacitance arrays, frequency dividing numbers M, N, and X and writingthese values to the ROM of IC 60. Needless to say, this frequencysetting apparatus may also have the function of inspecting the circuitboard, as mentioned above.

Probes 101 may be directly connected to terminals of the oscillator 5.However, special or ordinary patterns, such as pads 105, for contactwith probes 101 may be provided as shown in FIG. 16 to improve thereliability of the frequency setting operations.

In the conventional oscillators, as described with reference to theseexamples, combinations of frequency dividing numbers with respect to thefrequencies to be output are previously set in a memory and thefrequency of a signal output from the oscillator is determined by one ofthe combinations used. In contrast, according to the present invention,not based on the idea of previously setting combinations of frequencydividing numbers, frequency dividing numbers M, N, and X can be variablyset independent of each other. In the oscillator of the presentinvention, therefore, innumerable combinations of frequency dividingnumbers M, N, and X can be used, so that the number of frequenciesproducible by one oscillator can be largely increased by enablingselection of any suitable one of such combinations. It is, therefore,possible to provide an oscillator capable of covering a wide frequencyrange and obtaining an output signal with high accuracy by using ahigh-precision quartz resonator which is stable in performance, andwhich can be manufactured at a low cost. Moreover, the arrangementenabling free setting of frequency dividing numbers M, N, and X ensuresthat frequency dividing numbers M, N, and X can be set according to theresonant frequency of each quartz resonator employed, thus making itpossible to remove the troublesome steps for frequency adjustment, whichhave been necessary in the conventional art. Further, the adjustmentcircuit is provided to enable generation of output signals havingfrequencies which cannot be covered by only changing the frequencydividing numbers M, N, and X.

INDUSTRIAL APPLICABILITY

As described above, the present invention makes it possible to supply,in a short period and at a low cost, an oscillator capable of outputtinga signal of any frequency required by users, and to use a low-pricedquartz resonator capable of oscillating stably as a vibration source foran oscillator capable of outputting frequencies in a wide range.Consequently, it is possible to provide an oscillator suitable forcommunication apparatuses and information processors with whichoscillator performance more stable and accurate than that forconventional apparatuses is required.

What is claimed is:
 1. An oscillator comprising:a piezoelectricresonator; an oscillation signal output section that oscillates thepiezoelectric resonator and outputs an oscillation signal of a firstfrequency; a first programmable divider that divides the first frequencyof said oscillation signal by a first frequency dividing number toobtain a reference signal of a second frequency; a PLL circuit sectionthat receives said reference signal input thereto and obtains amultiplied signal of a third frequency, said PLL circuit sectionmultiplying said input reference signal by a second frequency dividingnumber from a second programmable divider provided in a feedback circuitto obtain said multiplied signal; and a setting section that variablysets said first frequency dividing number and said second frequencydividing number to values independent of each other, said piezoelectricresonator, said oscillation signal output section, said firstprogrammable divider, said PLL circuit section and said setting sectionbeing packaged integrally with each other, the oscillator furthercomprising a bypass circuit that directly outputs said oscillationsignal without passing the oscillation signal through the firstprogrammable divider and the PLL circuit section.
 2. The oscillatoraccording to claim 1, further comprising a third programmable dividerthat divides said multiplied signal by a third frequency dividingnumber,said setting section variably setting said third frequencydividing number to a value independent of said first frequency dividingnumber and said second frequency dividing number.
 3. The oscillatoraccording to claim 1, said oscillation signal output section having anadjustment circuit that finely adjusts said first frequency with respectto a resonant frequency of said piezoelectric resonator, andsaid settingsection setting an adjustment amount for said adjustment circuit.
 4. Theoscillator according to claim 3, said adjustment circuit having aplurality of weighted capacitance arrays.
 5. The oscillator according toclaim 3, said adjustment circuit having a variable-capacitance diode. 6.The oscillator according to claim 1,said setting section having aplurality of ROMs, and at least said first frequency diving number andsaid second frequency dividing number being set in one of said ROMs. 7.The oscillator according to claim 6, said oscillation signal outputsection having an adjustment circuit that finely adjusts said firstfrequency with respect to a resonant frequency of said piezoelectricresonator, andat least said first frequency dividing number and saidsecond frequency dividing number and an adjustment amount for saidadjustment circuit being set in one of said ROMs.
 8. The oscillatoraccording to claim 6, further comprising an input section that controlsan operating state of the oscillator, information designating a functionto be controlled by said input section being set in said ROMs.
 9. Anoscillator comprising:a piezoelectric resonator; an oscillation signaloutput section that oscillates the piezoelectric resonator and outputsan oscillation signal of a first frequency; a first programmable dividerthat divides the first frequency of said oscillation signal by a firstfrequency dividing number to obtain a reference signal of a secondfrequency; a PLL circuit section that receives said reference signalinput thereto and obtains a multiplied signal of a third frequency, saidPLL circuit section multiplying said input reference signal by a secondfrequency dividing number from a second programmable divider provided ina feedback circuit to obtain said multiplied signal; and a settingsection that variably sets said first frequency dividing number and saidsecond frequency dividing, number to values independent of each other,said piezoelectric resonator being a rectangular AT cut quartz resonatorthat oscillates a fundamental wave of 25.1 MHz.
 10. A frequency settingmethod for an oscillator comprising:measuring a resonant frequency of apiezoelectric resonator using a bypass circuit that directly outputs anoscillation signal without passing the oscillation signal through afirst programmable divider and a PLL circuit section; outputting theoscillation signal of a first frequency by finely adjusting the resonantfrequency of the piezoelectric resonator; outputting a reference signalof a second frequency by dividing the first frequency of the oscillationsignal by a first frequency dividing number; operating a PLL circuit byusing the reference signal as an input signal to the PLL circuit;forming a multiplied signal of a third frequency by multiplying saidinput signal by a second frequency dividing number from a secondprogrammable divider provided in a feedback circuit in the PLL circuit;setting, on a basis of sad resonant frequency unadjusted, said firstfrequency dividing number and said second frequency dividing number tonumbers that said third frequency of the multiplied signal is obtainedas a frequency closest to a desired frequency; and performing fineadjustment to adjust said third frequency equal to said desiredfrequency.
 11. The frequency setting method for an oscillator accordingto claim 10 setting said first frequency dividing number and said secondfrequency dividing number and performing, fine adjustment beingperformed after said oscillator has been mounted on a circuit board. 12.A frequency setting method for an oscillator comprising:outputting anoscillation signal of a first frequency by finely adjusting a resonantfrequency of a piezoelectric resonator; outputting a reference signal ofa second frequency by dividing the first frequency of the oscillationsignal by a first frequency dividing number; operating a PLL circuit byusing t he reference signal as an input signal to the PLL circuit;forming a multiplied signal of a third frequency by multiplying saidinput signal by a second frequency dividing number from a secondprogrammable divider provided in a feedback circuit in the PLL circuit;setting, on a basis of said resonant frequency unadjusted, said firstfrequency dividing number and said second frequency dividing number tonumbers that said third frequency of the multiplied signal is obtainedas a frequency closest to a desired frequency; and performing fineadjustment to adjust said third frequency equal to said desiredfrequency, setting said first frequency dividing number and said secondfrequency dividing number and performing fine adjustment being performedin a process of inspecting, by using probes, a circuit board on whichsaid oscillator is mounted.
 13. A frequency setting method for anoscillator comprising:measuring a resonant frequency of a piezoelectricresonator using a bypass circuit that directly outputs an oscillationsignal without passing the oscillation signal through a firstprogrammable divider and a PLL circuit section; outputting anoscillation signal of a first frequency by finely adjusting the resonantfrequency of the piezoelectric resonator; outputting a reference signalof a second frequency by dividing the first frequency of the oscillationsignal by a first frequency dividing number; operating a PLL circuit byusing the reference signal as an input signal to the PLL circuit;forming a multiplied signal of a third frequency by multiplying saidinput signal by a second frequency dividing number from a secondprogrammable divider provided in a feedback circuit in the PLL circuit;setting, on a basis of an ideal resonant frequency of said piezoelectricresonator, said first frequency dividing number and said secondfrequency dividing number to numbers that said third frequency of themultiplied signal is obtained as a frequency closest to a desiredfrequency; and finely adjusting, on a basis of said first frequencydividing number and said second frequency dividing number obtained, saidfirst frequency to a value that said desired frequency is obtained. 14.The frequency setting method for an oscillator according to claim 13,setting said first frequency dividing number and said second frequencydividing number and performing fine adjustment being performed aftersaid oscillator has been mounted on a circuit board.
 15. A frequencysetting method for an oscillator comprising:outputting an oscillationsignal of a first frequency by finely adjusting a resonant frequency ofa piezoelectric resonator; outputting a reference signal of a secondfrequency by dividing the first frequency of the oscillation signal by afirst frequency dividing number; operating a PLL circuit by using thereference signal as an input signal to the PLL circuit; forming amultiplied signal of a third frequency by multiplying said input signalby a second frequency dividing number from a second programmable dividerprovided in a feedback circuit in the PLL circuit; setting, on a basisof an ideal resonant frequency of said piezoelectric resonator, saidfirst frequency dividing number and said second frequency dividingnumber to numbers that said third frequency of the multiplied signal isobtained as a frequency closest to a desired frequency; and finelyadjusting, on a basis of said first frequency dividing number and saidsecond frequency dividing number obtained, said first frequency to avalue that said desired frequency is obtained, setting said firstfrequency dividing number and said second frequency dividing number andperforming fine adjustment performed in a process of inspecting, byusing probes, a circuit board on which said oscillator is mounted.
 16. Afrequency setting system for an oscillator, said frequency settingsystem outputting an oscillation signal of a first frequency by finelyadjusting a resonant frequency of a piezoelectric resonator, outputtinga reference signal of a second frequency by dividing the first frequencyof the oscillation signal by a first frequency dividing number,operating a PLL circuit by using the reference signal as an input signalto the PLL circuit to form a multiplied signal of a third frequency, themultiplied signal being obtained by multiplying said input signal by asecond frequency dividing number from a second programmable dividerprovided in a feedback circuit in the PLL circuit, said frequencysetting system comprising:a ROM that stores an amount of fine adjustmentof the resonant frequency and said first frequency dividing number andsaid second frequency dividing number; probes attachable to a circuitboard on which said oscillator is mounted; and a frequency settingapparatus that determines said fine adjustment amount and said firstfrequency dividing number and said second frequency dividing numberthrough said probes, and sets the fine adjustment amount and said firstfrequency dividing number and said second frequency dividing number insaid ROM.
 17. The frequency setting system for an oscillator accordingto claim 16, said frequency setting apparatus inspecting said circuitboard through said probes.